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ScienceGlobal issues

First image of black hole at center of Milky Way released

Esteban Pardo
May 12, 2022

Scientists theorize that "supermassive black holes" lie at the center of all galaxies, including our own. "Sagittarius A*" is orders of magnitude more dense than the sun but it's also quite some distance from Earth.

Black hole Sagittarius A*
A link of eight radio observatories form the virtual telescope that captured the first visual images of Sagittarius A*Image: Event Horizon Telescope collaboration

Image of black hole "in our own backyard" unveiled: astronomer Sara Issaoun

An international team of astronomers on Thursday unveiled the first image of a supermassive black hole called Sagittarius A*, or Sgr A*, at the center of the Milky Way. 

It comes three years after the very first image of a black hole from a distant galaxy was released. 

Black holes are regions of space whose gravity pull is so strong that nothing can escape it, including light.

"For decades, we have known about a compact object that is at the heart of our galaxy that is four million times more massive than our Sun," Harvard University astronomer Sara Issaoun told a press conference in Garching, Germany.

"Today, right this moment, we have direct evidence that this object is a black hole," she added.

Unravelling black holes

Within Milky Way but far away

The image was captured by the Event Horizon Telescope Collaborative and is the first direct visual rendering of the presence of this object, which is invisible to the naked eye.

The black hole itself is not depicted by the telescope's image, but rather the glowing gas that encircles it in a bright ring of light. 

Sagittarius A* has an estimated mass of 4 million times greater than Earth's Sun and a diameter of around the size of the orbit of Mercury — some 46 million kilometers.

Although it is within our Milky Way galaxy, the black hole is located an estimated 27,000 light years from earth — by comparison, the sun is a little more than 8 light minutes away from Earth.

EHT captured the image

To capture the image from Sagittarius A*, scientists had to link eight giant radio observatories across the planet to form a single "Earth-sized" virtual telescope, the Event Horizon Telescope (EHT).

"The EHT can see three million times sharper than the human eye," German scientist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy told reporters.

If we could see in the same way as the telescope, "when you are sitting in a Munich Biergarten, you could see the bubbles in a glass of bier in New York," Krichbaum said.

To capture the image, the EHT observed Sagittarius A* for multiple nights for many hours in a row, the same process used to produce the first image of a black hole in 2019.

Despite being closer to Earth, it was still difficult to capture the image. The brightness and pattern of the gas surrounding Sagittarius A* changed rapidly as the team observed it, "a bit like trying to take a clear picture of a puppy quickly chasing its tail," said EHT scientist Chi-kwan Chan of the University of Arizona.

Because of the distorting effects of Earth’s atmosphere, these observations need to be made in high-altitude, dry places like Chile’s Atacama Desert or high volcanoes in Hawaii.

Image of black hole "in our own backyard" unveiled: astronomer Sara Issaoun

What's going on at the center of our galaxy?

Since the 1930s scientists have been looking into the center of the Milky Way, located some 26,000 light-years from home in the direction of the Sagittarius constellation.

But because Earth is located in one of the arms of the Milky Way, there are gigantic clouds of interstellar gas and dust between us and the center, making it impossible to see through in normal light.

The American physicist Karl Jensky, considered by many one of the fathers of radio astronomy, first discovered a radio signal coming from this region, which was later called Sagittarius A.

In 1974, scientists discovered the waves were being emitted by a compact source, later coined Sagittarius A* .

Decades later, in the 1990s, observation methods developed to carefully and precisely measure the motion of stars orbiting Sagittarius A* gave us the best evidence so far that this very compact radio source was a supermassive black hole. 

jcg/msh (AFP, AP, dpa)

What is a black hole?